1/2 stick butter
2 lbs. frozen hash brown potatoes, thawed
1/4 c. mayonnaise
1 med. onion, chopped
10 oz. cheddar cheese, grated
1 c. sour cream
1 can cream of mushroom soup

Melt butter and saute onion. Add hash browns, cheese, sour cream, mayonnaise and soup. Bake in 8 x 13 inch casserole dish for 1 1/2 hours at 350 degrees. Serves 8 to 10. Freezes well.